The invention relates to a pipeline which is provided with a thermal insulation layer made of syntactic material. Syntactic material was initially developed as a buoyancy aid for deep-water submergence vehicles and consists of hollow microspheres in a polymeric matrix material. It has the advantage over foamed polymer in that it can, with the aid of high strength microspheres, be designed to withstand much greater hydrostatic pressures. The addition of the hollow microspheres also reduces the thermal conductivity of the material and therefore makes syntactic foam suitable for deeper water sub-sea flowline insulation.
In addition to having the necessary compressive strength and thermal conductivity, insulation for sub-sea flowlines must have adequate flexural performance to allow the coated pipe to be laid by any of the existing pipelaying methods including the use of a reel barge.
Hence the insulation material must be able to withstand a large tensile elongation without rupture.
It is known in the art that an increasing volume fraction of microspheres in the matrix material reduces the tensile stress at failure and that the mechanical strength of syntactic materials depends not only on the strength of the microspheres but also on their wettability with the resin. In view thereof, it has already been proposed to treat the microspheres with surface modification agents and to replace epoxide, polyurethane and polyester resins which are usually used as a matrix material by polyvinylchloride (PVC).
However, the tensile stress at failure of this existing syntactic material still requires improvement.